1. Field of the Invention
The present invention relates to a production method of a thin plate produced by cutting a foreign coin, an imitation of the foreign coin or the like as processing object, for use as an hour plate (a dial) of watch or the like, and a thin plate support for chucking to be employed in the method.
2. Description of the Related Art
Commonly owned Japanese Patent No. 3052133 discloses a production method of a thin plate to be used by attaching on outer peripheral surface of a cigarette lighter and various articles.
As shown in FIGS. 13 and 14, in the production method, a thin plate portion 1 in gear shape, for example and a chucking annular portion 2 surrounding the thin plate portion 1 and four connecting pieces 3 connecting between the thin plate portion 1 and the chucking annular portion 2 are initially formed on one side surface 5a of a base material portion 5 as an integral primary processed article a. The primary processed article a is set in a lathe turning machine provided with a receptacle cavity 6a with chucking by a chuck 6 for rotation. While the primary processed article a is driven to rotate by the lathe turning machine, the base material portion 5 is cut ands removed from the other side surface 5b to one side surface 5a by a cutting tool 7 to form a secondary processed article. Thereafter, the thin plate portion 1 is cut off from all of the connecting piece portions 1.
The applicant has attempted to produce an hour plate for the watch of so-called skeleton type using a coin as an application of the foregoing production method. For this purpose, as shown in FIG. 15, cutting is performed along a contour of three dimensional patterns 9, 10, 11a and 11b appearing on one side surface of a foreign coin 8 to form window openings 12a, 12b, 12c, 12d and 12e for viewing at least a part of a movement (not shown) between an external peripheral frame and the three dimensional pattern portions 9, 10, 11a and 11b. Also, machining process is effected for the other side surface for obtaining the thin plate in a thickness about 0.4 mm.
However, if attempt is made to form the hour plate of the watch by the production method the thin plate, it becomes necessary to directly chuck the outer peripheral portion of the foreign coin by a chuck 6 since the foreign coin 8 does not have a portion corresponding to the chucking annular portion 2 of the primary processed article a as shown in FIGS. 13 and 14.
Therefore, a binding force of the chuck 6 in inherently exerted the foreign coin directly to possibly cause deformation, such as bowing or the like associating with reduction of the late thickness according to progress of machining.
Particularly, upon machining or cutting the coin of noble metal, such as gold coin, sliver coin, or the like having relatively low hardness, in addition to bowing deformation, kink may be caused at the peripheral edge portion of the window opening to make machining difficult.
Furthermore, since the receptacle cavity 6a for receiving the coin is formed in the chuck, a lots of chucks corresponding to kinds of the coins has to be prepared. In addition, exchanging of the chucks per se is troublesome work.
The present invention has been worked out for solving the shortcoming in the prior art. Therefore, it is an object of the present invention to provide a production method of a thin plate and a thin plate support for chucking to be employed in the method, which can avoid occurrence of deformation, such as bowing, kink and so forth in a processing object, such as coin irrespective of hardness of the material and can form window openings around three-dimensional pattern to be maintained.
According to one aspect of the present invention, a production method of a thin plate comprises the steps of:
preparing thin plate support with a receptacle cavity having a bottom surface formed with a complementary three-dimensional pattern with a three-dimensional pattern on one side surface of a machining object;
setting the machining object within the receptacle cavity with mating the complementary three-dimensional pattern with the three-dimensional pattern on the one surface of the machining object;
chucking the thin plate support carrying the machining object set in the receptacle cavity on a machine tool;
driving the thin plate support together with the machining object to rotate; and
machining the machining object as being driven to rotate on the machine tool from the other side of the machining object by means of a cutting tool.
In the present invention set forth above, the machining object may be machined until the three-dimensional pattern being left and window openings being formed around the three-dimensional pattern. Thus, machining of the machining object and formation of the window openings are formed simultaneously.
On the other hand, the machining object is formed with a window opening defining grooves extending along the contour of the window openings, and the machining is performed by the cutting tool until the window opening defining grooves appear. Thus, formation of the window openings can be facilitated even when a height difference between the portions where the window openings are to be formed and the three-dimensional pattern portion.
On the other hand, the machining process is terminated before window openings are formed and the machining object is released from the thin plate support, and subsequently subject to cutting process for forming the thin plate maintaining the three-dimensional pattern and defining the window openings. By this process, even for the machining object having low hardness, such as gold coin, silver coin or the like, the window openings can be formed neatly.
The production method further comprise positioning means consisted of a pair of members, for mating and engaging a three-dimensional pattern portion of the machining object and the thin plate support for chucking, one of the members of the positioning means being provided on the machining object and the other of the members being provided in a receptacle cavity, the machining object being received with in the receptacle cavity with positioning by the positioning means for making the pair of members. Thus, positioning between the thin plate and the thin plate support for chucking can be done easily and in short period.
The machining object may be bonded and fixed within the receptacle cavity of the thin plate support for chucking by an adhesive for performing machining of the machining object. Thus, thin plate having thinner thickness than that formed conventionally can be formed without causing deformation, such as bowing.
The thin plate support bonded a thin plate or the machining object on machining within the receptacle cavity, may be dipped in a releasing agent for releasing the thin plate or the machining object on machining object from the receptacle cavity. By this, the thin plate or the machining object on machining can be released from the thin plate support without application of external force. Therefore, thin plate can be released without causing deformation.
According to another aspect of the present invention, a thin plate support for chucking provided with a receptacle cavity having a bottom surface formed with a mating portion mating with one side of a machining object.
In the preferred construction, the mating portion may be formed with a three-dimensional pattern complementary with a three-dimensional pattern of the machining object, the mating portion also has a ridge matching with a contour of a window opening to be formed and with a predetermined height. This facilitates formation of the window openings in the machining object.
A receptacle cavity and the machining object may be bonded by an adhesive while machined and the thin plate support is released the matching object by releasing agent penetrating therebetween. By this, the thin plate or the machining object on machining can be released from the thin plate support without application of external force. Therefore, thin plate can be released without causing deformation.